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From: Stefan Hajnoczi <stefanha@redhat.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Jens Axboe <axboe@kernel.dk>, Sargun Dhillon <sargun@sargun.me>,
	Kees Cook <keescook@chromium.org>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	Jann Horn <jannh@google.com>, Aleksa Sarai <asarai@suse.de>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	io-uring@vger.kernel.org,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Jeff Moyer <jmoyer@redhat.com>,
	Stefano Garzarella <sgarzare@redhat.com>
Subject: Re: [PATCH RFC 0/3] io_uring: add restrictions to support untrusted applications and guests
Date: Mon, 13 Jul 2020 10:24:35 +0100	[thread overview]
Message-ID: <20200713092435.GC28639@stefanha-x1.localdomain> (raw)
In-Reply-To: <20200710162017.qdu34ermtxh3rfgl@steredhat>

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On Fri, Jul 10, 2020 at 06:20:17PM +0200, Stefano Garzarella wrote:
> On Fri, Jul 10, 2020 at 11:33:09AM -0400, Konrad Rzeszutek Wilk wrote:
> > .snip..
> > > Just to recap the proposal, the idea is to add some restrictions to the
> > > operations (sqe, register, fixed file) to safely allow untrusted applications
> > > or guests to use io_uring queues.
> > 
> > Hi!
> > 
> > This is neat and quite cool - but one thing that keeps nagging me is
> > what how much overhead does this cut from the existing setup when you use
> > virtio (with guests obviously)?
> 
> I need to do more tests, but the preliminary results that I reported on
> the original proposal [1] show an overhead of ~ 4.17 uS (with iodepth=1)
> when I'm using virtio ring processed in a dedicated iothread:
> 
>   - 73 kIOPS using virtio-blk + QEMU iothread + io_uring backend
>   - 104 kIOPS using io_uring passthrough
> 
> >                                 That is from a high level view the
> > beaty of io_uring being passed in the guest is you don't have the
> > virtio ring -> io_uring processing, right?
> 
> Right, and potentially we can share the io_uring queues directly to the
> guest userspace applications, cutting down the cost of Linux block
> layer in the guest.

Another factor is that the guest submits requests directly to the host
kernel sqpoll thread. When a virtqueue is used the sqpoll thread cannot
poll it directly so another host thread (QEMU) needs to poll the
virtqueue. The same applies for the completion code path.

Stefan

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      reply	other threads:[~2020-07-13  9:24 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-10 14:19 Stefano Garzarella
2020-07-10 14:19 ` [PATCH RFC 1/3] io_uring: use an enumeration for io_uring_register(2) opcodes Stefano Garzarella
2020-07-10 14:19 ` [PATCH RFC 2/3] io_uring: add IOURING_REGISTER_RESTRICTIONS opcode Stefano Garzarella
2020-07-10 17:52   ` Jens Axboe
2020-07-13  8:07     ` Stefano Garzarella
2020-07-10 14:19 ` [PATCH RFC 3/3] io_uring: allow disabling rings during the creation Stefano Garzarella
2020-07-10 15:33 ` [PATCH RFC 0/3] io_uring: add restrictions to support untrusted applications and guests Konrad Rzeszutek Wilk
2020-07-10 16:20   ` Stefano Garzarella
2020-07-13  9:24     ` Stefan Hajnoczi [this message]

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